You can "seed" snaps.
Here is an example seeding the Gnome Calculator snap package. I tested this approach on Xubuntu 20.04.
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PREFORM THE FOLLOWING STEPS ON YOUR HOST COMPUTER...
1. Create the seed directory structure.
Execute the following:
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mkdir seed
cd seed
mkdir snaps
mkdir assertions
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2. Download the snaps.
The following additional snaps are required to install Gnome Calculator:
• core
• core18
• gnome-3-34-1804
• gtk-common-themes
Identifying required snap packages can be a trial and error process (as explained in step 12, below).
The core snap package is required because it is used by the model and account assertions (in step 4, below).
Depending on the snap package you are installing, you may need core18 (Ubuntu 18.04) or core20 (Ubuntu 20.04) . Gnome Calculator requires core18.
Execute the following:
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snap download core
snap download core18
snap download gnome-3-34-1804
snap download gnome-calculator
snap download gtk-common-themes
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3. Move the downloaded files to the correct directories.
Execute the following:
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mv *snap ./snaps
mv *assert ./assertions
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4. Create model and account assertions.
You only have to do this step once, even if you download additional snap packages.
Execute the following:
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cd ./assertions
snap known --remote model series=16 model=generic-
ACCOUNT_
snap known --remote account-key public-
snap known --remote account account-id=generic > generic.account
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5. Create a seed.yaml file.
Execute the following:
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cd ..
touch ./seed.yaml
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6. List the snaps so you can add them to the seed.yaml file.
Execute the following:
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ls -1 snaps
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Here is the output for this example.
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core_11167.snap
core18_
gnome-
gnome-
gtk-
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7. Open the new seed.yaml file in a text editor such as Gedit.
Add all of the snaps you had downloaded in step 2, using the following structure:
• The file starts with "snaps:"
• Each snap is separated by a line containing the dash (-) character
• The name is the part of the *.snap file before the underscore (_) character
• The channel should be stable (unless you downloaded from a different channel)
• The file is simply the full file name of the *.snap file
Here is the seed.yaml for this example.
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snaps:
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name: core
channel: stable
file: core_11167.snap
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name: core18
channel: stable
file: core18_2066.snap
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name: gnome-3-34-1804
channel: stable
file: gnome-3-
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name: gnome-calculator
channel: stable
file: gnome-calculato
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name: gtk-common-themes
channel: stable
file: gtk-common-
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PREFORM THE FOLLOWING STEPS USING CUBIC...
8. Launch Cubic.
9. Navigate to the Terminal page.
Change the current directory.
Execute the following:
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cd /var/lib/snapd
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10. Copy the snap seed files.
Open a file browser such as Nautilus.
Drag and drop the seed directory you created in step 1 onto the Cubic window in order to copy it into the current directory /var/lib/snapd.
11. Finish generating the custom ISO and exit Cubic.
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TESTING AND FINDING ERRORS...
12. Boot into your customized ISO.
Open a terminal.
Execute the following:
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snap warnings
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If the snap packages were installed successfully, you will see the message No warnings. Otherwise, you will see a message explaining the issue. If the snap you tried to seed requires another snap package, the missing snap package will be listed. In that case, add the missing package, as shown in step 2.
In my test, the Gnome Calculator icon was not initially displayed in the Applications list. However, after I launched the application from the command line, using gnome-calculator, the launcher icon was then added to the Applications list.
